There is known in the art a class of devices generally referred to as “scroll” pumps, compressors and expanders, wherein two interfitting spiroidal or involute spiral elements are conjugate to each other and are mounted on separate end plates forming what may be termed as fixed and orbiting scrolls. These elements are interfitted to form line contacts between spiral elements.
A pair of adjacent line contacts and the surfaces of end plates form at least one sealed off pocket. When one scroll, i.e. the orbiting scroll, makes relative orbiting motion, i.e. circular translation, with respect to the other, the line contacts on the spiral walls move along the walls and thus change the volume of the sealed off pocket. The volume change of the pocket will expand or compress the fluid in the pocket, depending on the direction of the orbiting motion.
Gas compression generates heat. Particularly, when air and gases with high specific heat ratio Cp/Cv are compressed, the heat generation is tremendous. In oil free compression, in order to achieve clean compressed gas, there is no oil, water or other lubricants and coolant allowed. However, the efficient removal of heat generated in the compression process is critical.
U.S. Pat. Nos. 5,842,843, 6,109,897 and 6,186,755 to Shuji Haga disclose a cooling means inside the drive shaft. The heat generated during compression can be removed at the central part of the compressor. The cooling means includes fans blowing cooling air directly towards the end plates of stationary scroll members. In some embodiments, the cooling means includes eccentrically installed heat pipes in the central portion of the drive shaft. In other embodiments, the cooling means includes an air passage in the central portion of the drive shaft to provide cooling air to enhance the cooling effects.
However, these designs have several shortcomings. First, the cooling fans directly blow cooling air to nearby endplates of stationary scroll members. The impinging flow to the endplate creates reverse flow and vortices that prevent cooling air from reaching the entire surface of the endplate needing cooling. Second, there are at most two heat pipes which can be installed in the central region of the drive shaft and the heat pipe condensers cannot be well cooled by cooling air because they are located inside the drive shaft that leads to low heat dissipation efficiency of the heat pipes. Third, the cooling air in the passage inside the drive shaft is driven by a centrifugal effect determined by the radial distance of the shaft OD which is fairly small. The cooling air is also driven by the low pressure upstream the fans that is also small. In other words, the cooling air flow inside the passage of the drive shaft is weak. Furthermore, the heat generated inside the scroll members is conducted to the shaft by overcoming a contact heat resistance between the scroll members and the shaft, and then is transferred by convection to the cooling air in the central hole of the drive shaft. This makes the heat dissipation from scroll members to the cooling air inefficient.
Referring to U.S. Pat. No. 6,905,320 B2 to Tohru Satoh, et al, an air cooling system provides transverse cooling air passing through the cooling fins on the opposite side of the scroll elements to cool the orbiting and fixed scroll. This cooling system needs an independent cooling fan to provide cooling air in the transverse direction and thus increases the cross sectional dimension. In addition, this cooling system does not provide cooling to the motor which usually need a separate cooling system.
U.S. Pat. No. 7,329,108 to Masaru Tsuchiya, et al. discloses a blowing fan between the orbiting scroll and the motor. This fan provides cooling air to the back of the fixed scroll, the crank handles and their bearings. However, the cooling fan system interrupts the motor shaft and the scroll driving shaft which will cause alignment difficulty. Furthermore, due to the zigzag of the cooling air passages, the cooling air experiences tremendous pressure loss that will seriously reduce the cooling air flow rate. Furthermore, there are air passages located downstream of the cooling fan. This arrangement of air passages creates significant pressure resistance to the fan and reduces the cooling air flow rates.
The prior art mentioned above does not provide sufficient cooling to the scrolls, bearings and motors. A more robust cooling system is necessary.